Since the semiconductor material (typically GaN, InGaN, AlN, Al—GaN, etc.) of high-power LEDs lack good thermal conductivity, high light powers have to be realized by assembling several LED chips into arrays. The conventional technique for assembling such arrays is by soldering or gluing LED chips (with or without subcarrier) with powers of 0.5 to 5 W using SMD techniques as a matrix on aluminum core circuit boards (typically in an equidistantial grid arrangement). Because of the limited thermal conductivity of aluminum (typically λAl=75-235 Wm−1K−1) distances of typically 20 to 30 mm between the chips have to be maintained—even if the aluminum core circuit board is directly coupled to a powerful cooling system. Therefore, the brilliance and power density of such solutions is limited. If, for example, atypical modern LED array with 5×5 LEDs of 5 W each is arranged in an area of 1 dm2 (100 cm2), a power of 125 W with the average power density of S=1.25 W/cm2 is achieved. For many applications, this is simply not enough. Furthermore, it is difficult to realize non-planar LED arrays with acceptable light guiding quality in this manner.
In EP 2665092 an LED substrate on a base of pure copper with a thin, highly thermally conductive dielectric is shown, which allows for a fourfold power density as compared to aluminum substrates (λCu999=401 Wm−1K−1). In this manner, the achievable power density rises to S=5 W/cm2, and densely packaged LED clusters of up to four 4 W LED chips arranged directly side-by-side can be built. This has, for example, made it possible to build LED spots with 3×4×4 W=48 W (three clusters of four LEDs and 4 W/LED), which, when focussed by means of TIR lenses, have beam characteristics and electrical power data similar to a MR16-50 W halogen lamp—but yield much more light. However, this system called COC (chip-on-copper) quickly reaches its limit with more than four clustered 4 W-LEDs because copper is a way too poor heat conductor. Low-glare high-powered street lamps with light distribution curves comparable to those of sodium high pressure vapour lamps (HPS) require, however, system powers of 100 to 400 W, and namely with linear LED arrays (clusters of linear light sources) with beamer dimensions of approximately 2.5×38 mm per 50 W module (4.5×38 mm for a 100 W module) and Lambert beam characteristics. This corresponds to a power density of S=52 W/cm2 or 58 W/cm2—i.e. more than ten times above the power densities achieved so far—which corresponds, by the way, to the power density of the solder lamp of a roofer. Furthermore, it should be possible to arrange the arrays in non-planar (i.e. three-dimensional) geometry to be able to build them into symmetric-parabolic and half-ellipsoidal reflectors of pure aluminum in order to maintain the required low amount of glare.